The present invention relates to magnetic circuits and more particularly to a magnetic circuit suitable as the driver unit of a planar diaphragm type loudspeaker.
It is known in the art that a planar diaphragm loudspeaker has a relatively flat acoustic pressure characteristic throughout its frequency range and accordingly can reproduce sounds with stable acoustic images. A variety of loudspeakers employing such planar diaphragms have been proposed in the art. Since planar diaphragm type loudspeaker systems of relatively large diameter can be readily manufactured, planar diaphragms are suitable for manufacturing high power loudspeaker systems.
However, employment of a large diameter diaphragm involves problems such as the provision, at a low manufacturing cost, of a driver unit which can sufficiently operate a large diaphragm. More specifically, since a large diameter bass-range diaphragm needs a large driver unit, it has proven rather difficult to assemble such a driver unit. For instance, large magnetic circuits require large plates and magnets. For a square planar diaphragm, a large, frame-shaped magnetic circuit is required. Such a large magnetic circuit is intricate in construction. Accordingly, it is difficult to assemble and process such a large magnetic circuit.
In a conventional linear type magnetic circuit, the magnetic flux from the magnet is introduced through the plate to the field system. That is, the conventional linear type magnetic circuit employs a circular external magnet type magnetic circuit. Accordingly, its magnetic flux leakage coefficient and electromotive force loss are undesirably high and its efficiency is low.